FIELD OF THE INVENTION
The invention relates to a modular promoter construct based on exon 1 of the actin 1 gene from rice.
There has always been the need to provide agronomically important cereal plants with improved properties. Previously, hereditary traits or genes were crossed into the plants concerned using classical methods. Since recombinant DNA technology has become established, it is possible to insert defined genes into the genome of cereal plants such as, for example, rice, maize, wheat and barley. In addition to selecting the correct selective marker gene and the agronomically important genes, the choice of the correct promoter is of crucial importance for effectively expressing the desired gene. The promoter which is used most for increasing the expression of chimeric genes in monocotyledonous cereal plants derives from the cauliflower mosaic virus (CaMV) 35S RNA gene (Odell et al., Nature 313, pages 810 to 820, 1985). However, as compared with its activity in dicotyledonous plants, this promoter is not very active in monocotyledonous plants (Topfer et al., Meth. Enzymol., "Rec. DNA", in press). Thus, alternative gene expression vectors using strong promoters, such as the promoters of the actin 1 gene from rice (McElroy et al., Plant Cell 2, pages 163 to 171, 1990) and the ubiquitin gene from maize (Christensen and Fox, International Society for Plant Molecular Biology Meeting, Program Abstracts, No. 287, 1991).
In analogy with animal systems (Dynan, Cell 58, pages 1 to 4, 1989), it is probably also the case for plant genes as well that the transcription mediated by RNA polymerase II is dependent on modular elements, i.e. elements consisting of different regulatory DNA sequences. It has already been demonstrated that a number of different modular elements play an important role in, for example, tissue-specific transcription (Katagiri and Chua, Trends Gent. 8, pages 22 to 70, 1992).
Thus, DE-OS 41 24 537 discloses a modular promoter construction which can be used to increase the expression of foreign genes in plant cells. In this case, a DNA sequence from exon 1 of the sucrose synthase gene from Zea mays L. is inserted between the promoter and the gene to be expressed. A further, multiplicative increase in gene expression is possible if an additional DNA sequence, corresponding essentially to intron 1 of the sucrose synthase gene from Zea mays L., is coupled to the said DNA sequence.
McElroy et al., loc. cit., have described the isolation of promoter sequences of the rice actin 1 gene lying in the 5' region. It has emerged that there is a positive correlation between the promoter sequences and the subsequent intron sequences. Thus, in investigations of the transformation of rice protoplasts, a promoter construct of these sequences has proved to be an effective regulator of the constitutive expression of a foreign gene.